Valley Flashing

I found the site yesterday searching for DIY websites.
I need help and have a question

While I've done many DIY projects I've never done roofing on a house before, so I had a contractor do the roof and gutter work.

I noticed today when they did the front of the house they didn't use flashing in the valley's. I told the contractor I've never seen it done this way and he said some roofers do and some don't. In driving my neighborhood all houses had flashing except on small front porches.

Do the valley's require flashing? Is it really possible to not be done with flashing

From Ohio and the pitch is very easily walkable

Thanks for any help
Roger